Organic solar cells contribute immensely towards the renewable source of energy generation at low cost and research in this area is increasing exponentially every year (Shen et al., Macromolecules 2013, 46, 9575-9586). Organic solar cells are regarded as potentially environment cordial source of power compared to other methods of energy production. Organic solar cells comprise of heterostructure of two semiconductor components with different and compatible energy levels. Bulk heterojunction is the most conventional geometry where the active layer comprises of donor and acceptor molecules sandwiched between a low workfunction and high workfunction electrodes which collect electrons and holes respectively. So far the intensive research efforts have produced the solar cells with efficiency as high as 10.6% (You et al., Nature Comm. 2012, 4:1446, 1-10). The most commonly used fullerene based acceptor material is [6,6]-Phenyl-C61-butyric acid methyl ester (PC61BM) particularly for polymer based organic solar cells and transistors (Scharber et al., Adv. Mater. 2006, 18, 789). Reported methods of PC61BM synthesis involves the dipolar cycloaddition reaction of diazoalkane which are generated insitu via base induced decomposition of tosylhydrazone derivative with 35% yield as the highest (Hummelen et at., J. Org. Chem. 1995, 60, 532; Lenes et al., Adv. Mater. 2008, 20, 2116) using pyridine and sodium methoxide under inert atmosphere for diazomethane generation. US patent number 2014/0066647 discloses the highest possible yield for PC61BM to be 40% on optimizing the fullerene, hydrazone and sodium methoxide ratios in pyridine. However, the most needful aspect of their application on large scale has been neglected which is, the impact on environment due to disposals during material synthesis (Daniel et al., Energy Environ. Sci., 2013, 6, 2053). A general catalytic procedure for the cycloaddition of diazo amides to fullerene[60] in the presence of the three-component catalyst, Pd(acac)2-PPh3-Et3Al, was reported by Tuktarov et al., (Tetrahedron Lett. 2013, 54, 2146) where, depending on the reaction conditions, pyrazolinofullerenes or methanofullerenes were formed. The inventors have previously reported the synthesis of PC61BM (RSC Adv. 2014, 4, 15675) in presence of triethyl amine as catalyst in dichloromethane under air in ˜40% yield. The limitations with the process were, low yield and use of chlorinated solvents. An eco-friendly and cost-effective methodology with high yield is essentially required to mitigate the environmental externalities of manufacturing on large scale for such materials. Also, there is a need of alternate material with better performance and should also mimic the structure of PC61BM to retain its inherent electrical and film properties. In this regard, we have come up with a process of synthesis of new fullerene derivative, i.e., [6,6]-phenyl-C61-butyric acid pentyl ester (PC61BP) under the present invention using different types of amines (secondary and tertiary) in ethyl acetate as well as in dichloromethane for better yields and properties in organic solar cells.